This invention relates to image pickup apparatus for providing a video signal, and is particularly directed to a solid-state image pickup device incorporating a current amplifier for converting a relatively feeble video signal to a strong video output signal with a high signal-to-noise (S/N) ratio.
A solid-state image pickup element, such as an MOS imager, generally provides a quite weak signal which must be amplified before being applied to a successive stage. This weak video signal is particularly susceptible to noise due to stray currents, shot noise, and the like. In an MOS imager, the video signal is provided as a diffentiated current. This signal must be integrated to obtain an average value, but integration lowers the overall level of the video signal. Thus, the integrated signal has a rather low S/N ratio.
An external amplifier is conventionally provided to amplify the output signal and thereby convert it to a level suitable for further processing. Unfortunately, this external amplifier amplifies the noise along with the video signal, and because it is external, also adds noise. Consequently, the resulting video output signal has a further deteriorated S/N ratio.